1. Field of the Invention
The invention relates to stoppered vacuum tubes and more particularly to a tube provided with one or more vents around the mouth to allow evacuation.
2. Brief Description of the Prior Art
It has been desirable from the standpoint of assembly and economics to place a vent in the stopper for vacuum tubes to allow evacuation of the tubes. Such vented stopper is pre-positioned in a glass tube, allowing only a required length of slot exposed to the atmosphere which is necessary for removal of air in the tube. Upon removal of air, the stopper is driven up to its shoulder and seals the tube from the atmosphere. Some of the problems inherent in such design are as follows:
(a) The construction of the stopper is subject to cell entrapment or attachment to the slot;
(b) The stopper seal is vulnerable to lateral load which can occur in handling or processing, and result in a zero draw tube; and
(c) Reliability in pre-placement depth control is required to prevent positive pressure tubes.
The prior art revealed the following U.S. Patents: Mond No. 1,399,394 which discloses a graduated glass tube having a pour spout at one end and a stopper inserted in the opposite flared end, and Silverstolpe No. 2,649,245 which allows a tubular vessel stoppered at both ends and in several embodiments shows slots in the outer stopper wall or passageways through the central portion of the stopper. Neither patent has any suggestion of a vent passageway on the tube structure.